Automatic frequency control circuit applicable to a mobile communication system

ABSTRACT

An automatic frequency control circuit comprises an quadrature demodulation unit for creating an in-phase signal and an antiphase signal by quadrature-demodulating a Gaussian Minimum Shiftkeying signal and supplying an electric field strength signal exhibiting an electric field strength of the Gaussian Minimum Shiftkeying signal as well as the created in-phase and antiphase signals; a quality judging unit for judging the quality of the Gaussian Minimum Shiftkeying signal and creating an automatic frequency-controlling data indicating a compensation amount in accordance with the obtained quality signal; a converter for converting into digital signals the in-phase signal, antiphase signal and electric field strength signal supplied from the quadrature demodulation unit and converting the automatic frequency-controlling data into an analog signal; a temperature compensated crystal oscillation circuit for compensating the frequency of the GMSK signal on the basis of the compensation amount indicated by the automatic frequency-controlling data converted into an analog signal by the converter.

BACKGROUNDS OF THE INVENTION

1. Field of the Invention

The present invention relates to an automatic frequency control circuitapplicable to a mobile communication system, and more particularly to anautomatic frequency control circuit for performing a frequency controlsuch as to deal with Doppler shift, multipass fading or the like whichoccurs during the movement of the mobile communication system.

2. Description of the Related Art

This kind of a conventional automatic frequency control circuit isdisclosed in Japanese Unexamined Patent Publication (Kokai) No. Heisei2-44886. The important part of the automatic frequency control disclosedin this article is shown in FIG. 3.

In FIG. 3, a timing signal "T" for controlling counting movement issupplied from a timing signal generation circuit 102 to a counter 100for counting an error detecting signal "C" from a PCM decoder 101. Aninhibit circuit includes the counter 100, the timing signal generationcircuit 102 and a judging circuit 110. The judging circuit 110 includesa latch circuit 111, a reference value generation circuit 112 and acomparison circuit 113.

A comparison unit 120 compares a count value from a counter 121 with areference value from a reference value generation circuit 122, so as tosupply a three-valued signal. The output signal "C" from the comparisonunit 120 is supplied to a gate circuit 130. The gate circuit 130prohibits the output signal "C1" of the comparison unit 120 from beingsupplied to a control circuit 131 if receiving from the comparison unit113 such a high level signal as indicating that the count value of thecounter 100 is more than the reference value.

More specifically, if the output value (count value) of the latchcircuit 111 is more than the reference value as the result of thecomparison of the comparison unit 113, the output of the comparison unit113 is at a H level, the gate circuit 130 is closed to prohibit thecomparison output "C1" of the comparison unit 120 from being supplied tothe control circuit 131, thereby prohibiting the automatic frequencycontrol operation.

The above-mentioned conventional automatic frequency control circuit isconstituted in that the gate circuit 130 prohibits supplying the outputsignal of the comparison unit 120 to the control circuit 131 ifreceiving from the comparison unit 120 the high level signal indicatingthat the count value of the counter 100 is more that the referencevalue. Therefore, if Doppler shift, multipass fading or the like occursduring the movement of the system to affect the received signal, such amalfunction may occur in the conventional automatic frequency controlcircuit that the comparison unit 120 outputs a signal of high level andthe gate circuit 130 prohibits the automatic frequency controloperation.

SUMMARY OF THE INVENTION

The first object of the present invention is to provide an automaticfrequency control circuit free from the malfunction caused by Dopplershift, multipass fading or the like, even if it may occur during themovement of a mobile communication system.

According to one aspect of the invention, an automatic frequency controlcircuit installed on a mobile communication system, comprising:

an quadrature demodulation means for creating an in-phase signal and anantiphase signal by quadrature-demodulating a Gaussian MinimumShiftkeying signal being supplied to said means, and supplying anelectric field strength signal exhibiting an electric field strength ofthe Gaussian Minimum Shiftkeying signal as well as said created in-phaseand antiphase signals,

a quality judging means for judging the quality of the Gaussian MinimumShiftkeying signal on the basis of said in-phase signal, antiphasesignal and electric field strength signal, and creating an automaticfrequency-controlling data indicating a compensation amount inaccordance with the obtained quality signal so as to supply the same,

a conversion means for converting said in-phase signal, antiphase signaland electric field strength signal supplied from said quadraturedemodulation means into digital signals so as to transfer them to saidquality judging means, and converting said automaticfrequency-controlling data supplied from said quality judging means intoan analog signal, and,

a compensating means for compensating the frequency of the GaussianMinimum Shiftkeying signal on the basis of the compensation amountindicated by said automatic frequency-controlling data converted into ananalog signal by said conversion means.

In the preferred construction, the quadrature demodulation meanscomprises a means for mixing the Gaussian Minimum Shiftkeying signalconverted to a first intermediate frequency signal and an oscillationsignal supplied from said compensating means on the basis of saidautomatic frequency-controlling data so as to convert them to a secondintermediate frequency signal, and a means for quadrature-modulating thesecond intermediate frequency signal so as to create said in-phasesignal and antiphase signal.

In the preferred construction, the quality judging means comprises ameans for calculating an amount of interference between codes on thebasis of said in-phase signal and antiphase signal, a means forcalculating the quality of the signal by the combination of said codesinterference amount and said electric field strength signal with theboth as parameter, and a means for supplying said automaticfrequency-controlling data indicating an compensation amount inaccordance with the quality of the signal to said conversion means.

In another preferred construction, the quality judging means comprises amutual-correlation factor calculating circuit for calculating themutual-correlation factor of the input signal on the basis of saidin-phase and antiphase signals to compute an amount of interferencebetween codes, a signal quality calculating circuit for calculating thequality of the signal by the combination of said codes interferenceamount and said electric field strength signal with the both asparameter, a signal quality judging circuit for ranking the quality ofthe signal and supplying the control signal exhibiting a rank of thecorresponding quality signal, and an automatic frequency-controllingdata creating circuit for creating an automatic frequency-controllingdata on the basis of said control signal.

In the above-mentioned construction, the mutual-correlation factorcalculating circuit obtains eleven mutual-correlation factors byshifting across central continuous 16 bits among 26 bits of trainingsequence codes in one burst of the in-phase signal on the basis of theGSM, selects arbitrary five mutual-correlation factors from the obtainedeleven mutual-correlation factors to totalize the absolute valuesthereof, and subtracts a total of the absolute values of the other sixmutual-correlation factors from a total of the absolute values of allthe eleven mutual-correlation factors, except for the fivemutual-correlation factors having the absolute values of which total ismaximum, thereby to transmit the obtained value as a codes interferenceamount signal.

In the above-mentioned construction, the signal quality calculatingcircuit

having a table relating a combination of said codes interference amountand electric field strength signal to a numerical value predetermined torepresent the quality of the input signal with the both as parameter,

combines said codes interference amount calculated by saidmutual-correlation factor calculating circuit and said electric fieldstrength signal supplied via said conversion means and checks them withsaid table, thereby to transmit the corresponding numerical value as aquality signal representing the quality of the corresponding inputsignal.

In the above-mentioned construction, the signal quality judging circuitranks the quality of the input signal calculated by said signal qualitycalculating circuit, and transmits a control signal for controlling saidautomatic frequency-controlling data creating circuit in order toperform the predetermined compensation to said automaticfrequency-controlling data in accordance with the quality rank of thecorresponding signal.

In the above-mentioned construction, the compensating means comprises avoltage controlled oscillation circuit for transmitting a predeterminedsignal which is used for the quadrature demodulation of the GaussianMinimum Shiftkeying signal in said quadrature demodulation means, atemperature compensated crystal oscillation circuit for creating andsupplying a compensation signal on the basis of said automaticfrequency-controlling data, and a phase lock loop circuit forcontrolling the oscillation frequency of said voltage controlledoscillation circuit according to the compensation signal supplied fromsaid temperature compensated crystal oscillation circuit; and

the quadrature demodulation means comprises a means for mixing theGaussian Minimum Shiftkeying signal converted to a first intermediatefrequency signal and an oscillation signal supplied from said voltagecontrolled oscillation circuit of said compensating means so as toconvert them to a second intermediate frequency signal, and a means forquadrature-modulating said second intermediate frequency signal so as tocreate said in-phase signal and antiphase signal.

Other objects, features and advantages of the present invention willbecome clear from the detailed description given herebelow.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given herebelow and from the accompanying drawings of thepreferred embodiment of the invention, which, however, should not betaken to be limitative to the invention, but are for explanation andunderstanding only.

In the drawings:

FIG. 1 is a block diagram showing a constitution of an automaticfrequency control circuit according to the first embodiment of thepresent invention.

FIG. 2 is a flow chart showing an operation of the embodiment.

FIG. 3 is a block diagram showing a constitution of a conventionalautomatic frequency circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will now be described indetail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the constitution of an automaticfrequency control circuit according to the embodiment of the invention.

As shown in FIG. 1, the automatic frequency control circuit of theembodiment comprises an quadrature demodulation unit 10 for receiving aGMSK (Gaussian Minimum Shiftkeying) signal "S1" to quadrature-demodulatethe same, a quality judgment unit 30 for judging the quality of the GMSKsignal "S1", a converter 20 for carrying out digital to analog or analogto digital conversion of a signal between the quadrature demodulationunit 10 and the quality judgment unit 30, a temperature compensatedcrystal oscillation circuit (TCXO) 41 for compensating the frequency ofthe GMSK signal "S1" on the basis of a result of judgment by the qualityjudgment unit 30, and a voltage controlled oscillation circuit (VCO) 42.It is noted here that FIG. 1 shows only characteristic parts of theconstitution in the embodiment, while the description of the otherconstitution is omitted.

The quadrature demodulation unit 10 includes a mixer 11 for receivingthe GMSK signal "S1" converted to a first intermediate frequency signaland converting it to a second intermediate frequency signal, a frequencydemultiplier 12, a frequency demultiplier 13 for quadrature-modulatingthe second intermediate frequency signal so as to create an in-phasesignal "I" and an antiphase signal "Q", amplifiers 14, 15 and 17, mixers16 and 18, and a phase shifter 19.

The GMSK signal "S1" received and converted to the first intermediatefrequency signal by a mobile communication receiver is supplied to themixer 11. The mixer 11 mixes a frequency divided signal by the frequencydemultiplier 12 with the GMSK signal "S1" so as to create the secondintermediate frequency signal "S2".

A signal is supplied from the voltage controlled oscillation circuit 42to the frequency demultiplier 12. The frequency demultiplier divides thefrequency of the signal by n1. The obtained frequency-divided signal istransferred to the mixer 11. It is noted here that n1 is an arbitrarywhole number.

Further, a signal is supplied from the voltage controlled oscillationcircuit 42 to the frequency demultiplier 13. The frequency demultiplier13 divides the frequency of the signal by n2. The obtainedfrequency-divided signal is transferred to the phase shifter 19. It isnoted here that n2 is an arbitrary whole number different from n1.

Provided at subsequent stages of the mixer 11 are the mixer 16 includingthe amplifier 14 at its input side and the amplifier 15 at its outputside, the mixer 18 including the amplifier 14 at its input side and theamplifier 17 at its output side, and the phase shifter 19 for convertingthe phase of the second intermediate frequency signal "S2" supplied tothe mixers 16 and 18.

The second intermediate frequency signal "S2" is supplied from the mixer11 to the mixer 16 via the amplifier 14. The mixer 16 creates thein-phase signal "I" having the same phase as the second intermediatefrequency signal "S2", and transmits it via the amplifier 15.

Also, the second intermediate frequency signal "S2" is supplied from themixer 11 to the mixer 18 via the amplifier 14. The mixer 18 creates theantiphase signal "Q" of which phase is shifted at an angle of 90° withrespect to the in-phase signal "I" supplied from the mixer 16. The mixer18 supplies the antiphase signal "Q" via the amplifier 17.

The phase shifter 19 shifts the phase of the second intermediatefrequency signal "S2" supplied to the mixer 18 at an angle of 90° withrespect to the phase of the second intermediate frequency signal "S2"supplied to the mixer 16, thereby creating the in-phase signal "I" andthe antiphase signal "Q".

The quadrature demodulation unit 10 transmits to the converter 20 thein-phase signal "I" and the antiphase signal "Q" thus created, as wellas an electric field strength signal "RSSI" supplied from the amplifier14.

The converter 20 includes an A/D conversion circuit 21, a D/A conversioncircuit 22, and a PLL (Phase Lock Loop) circuit 23.

The A/D conversion circuit 21 converts the in-phase signal "I", theantiphase signal "Q" and the electric field strength signal "RSSI"transmitted from the quadrature demodulation unit 10 into digitalsignals so as to send them to the quality judgment unit 30.

The D/A conversion circuit 22 converts into an analog signal anautomatic frequency-controlling data (referred to as AFC datahereinafter) signal "S3" transmitted from the quality judgment unit 30,which data will be described below. The D/A conversion circuit 22 sendsthe AFC data signal to the temperature compensated crystal oscillationcircuit 41.

The PLL circuit 23 controls the voltage controlled oscillation circuit42 on the basis of a compensation signal "S4" from the temperaturecompensated crystal oscillation circuit 41.

The quality judgment unit 30 includes a mutual-correlation factorcalculating circuit 31 for calculating the mutual-correlation of theinput signals, a signal quality calculating circuit 32 and a signalquality judging circuit 33 for judging the quality of the input signalon the basis of the calculated mutual-correlation of the input signal,and an AFC data creating circuit 34 for creating an AFC data inaccordance with the quality of the input signal.

The in-phase signal "I" and the antiphase signal "Q" converted to thedigital signals are supplied to the mutual-correlation factorcalculating circuit 31. The circuits 31 calculates themutual-correlation factor of the input signal to compute an amount ofinterference between codes. Concretely, the codes interference amount iscomputed in the following manner. At first, in the GSM(Global System forMobile communication), central continuous 16 bits among 26 bits oftraining sequence codes in one burst of the in-phase signal "I" areshifted across, thereby to obtain eleven mutual-correlation factors.Arbitrary five mutual-correlation factors are selected from the obtainedeleven mutual-correlation factors and the absolute values thereof aretotalized. Except for the five mutual-correlation factors having theabsolute values of which total is maximum, a total of the absolutevalues of the other six mutual-correlation factors is subtracted from atotal of the absolute values of all the eleven mutual-correlationfactors. The obtained value is supplied to the signal qualitycalculating circuit 32 as the codes interference amount signal "S5".

Essentially, the 16 bits corresponding to the six mutual-correlationfactors having the absolute values whose total is maximum, arepositioned at the center of the 26 bits of the training sequence codesunless the quality of the input signal is deteriorated. When the inputsignal is degraded in quality, the above 16 bits are shifted. Therefore,it can be detected by the above operation whether the quality of theinput signal is deteriorated or not.

The signal quality calculating circuit 32 determines the quality of theinput signal on the basis of the amount of interference between thecodes exhibited by the codes interference amount signal "S5" suppliedfrom the mutual-correlation factor calculating circuit 31 as well as theelectric field strength signal "RSSI". To be concrete, the quality ofthe input signal is determined as follows. That is to say, the signalquality calculating circuit 32 has a table which relates a combinationof the codes interference amount and the electric field strength signal"RSSI" to a numerical value predetermined to represent the quality ofthe input signal, with the codes interference amount and the electricfield strength signal "RSSI" as parameter. The amount of interferencebetween the codes of the input signal exhibited by the codesinterference amount signal "S5" calculated by the mutual-correlationfactor calculating circuit 31 and the electric field strength signal"RSSI" of the input signal supplied from the A/D conversion circuit 21of the converter 20 are combined and checked with the table, and thecorresponding numerical value is supplied to the signal quality judgingcircuit 33 as a quality signal "S6" representing the quality of theinput signal.

The signal quality judging circuit 33 evaluates the quality of the inputsignal on the basis of the quality signal "S6" from the signal qualitycalculating circuit 32, and controls the AFC data creating circuit 34.More specifically, there are provided several ranks for evaluating thequality of the input signal, and it is judged which rank the qualitysignal "S6" of the input signal is in. A control signal "S7" forcontrolling the AFC data creating circuit 34 is supplied in order toperform a predetermined compensation to the AFC data in accordance withthe quality rank of the quality signal "S6".

The AFC data creating circuit 34 compensates the AFC data on the basisof the control signal "S7" from the signal quality judging circuit 33,so as to create and supply the AFC data signal "S3". The output AFC datasignal "S3" is not only utilized by the mobile communication systembody, but also transferred to the D/A conversion circuit 22 of theconverter 20. The AFC data is compensated by multiplying the AFC data bya compensation factor previously set in correspondence with every rankof the quality of the input signal.

A more detailed description will be made about the judgment of thequality of the input signal by the signal quality judging circuit 33 andthe compensation of the AFC data performed by the AFC data creatingcircuit on the basis of that quality judgment.

More specifically, the signal quality judging circuit 33 fixes on thequality of the input signal either of eleven ranks between "10"exhibiting the highest quality and "0" exhibiting the lowest quality.The AFC data creating circuit 34 regards the ranks "3" and below asinferior quality and compensates the input signal in the same mannerwhen any of the ranks "3" and below is fixed on the quality of the inputsignal. In this case, if the signal quality judging circuit 33 decidesthat the quality signal "S6" delivered from the signal qualitycalculating circuit 32 corresponds to the rank "10", the signal qualityis kept by 100%. The AFC data creating circuit 34 multiplies the AFCdata by a compensation factor predetermined in accordance with thequality. Then, the AFC data creating circuit 34 supplies the AFC datasignal "S3" thus obtained.

In the case where the signal quality judging circuit 33 judges that thequality signal "S6" transmitted from the signal quality calculatingcircuit 32 corresponds to a rank "7", the signal quality is kept by 70%.The AFC data creating circuit 34 multiplies the AFC data by acompensation factor predetermined in accordance with the quality. Then,the AFC data creating circuit 34 supplies the AFC data signal "S3" thusobtained.

Further, if the signal quality judging circuit 33 judges that thequality signal "S6" transmitted from the signal quality calculatingcircuit 32 corresponds to the rank "3", the signal quality is kept by30%. Because the AFC data creating circuit 34 treats the quality in therank "3" and below as the same inferior quality, the AFC data creatingcircuit 34 multiplies the AFC data by a compensation factorpredetermined in accordance with the quality in the rank "0". Then, theAFC data creating circuit 34 supplies the AFC data signal "S3" thusobtained.

Incidentally, how many ranks there provided for evaluating the qualityof the input signal and how a compensation factor corresponding to eachquality rank is predetermined, can be appropriately decided inaccordance with the constitution or purpose of use of the mobilecommunication system, the frequency of an input signal to be dealt withby the communication system, or the like.

The AFC data signal "S3" converted to the analog signal by the D/Aconversion circuit 22 of the converter 20 is supplied to the temperaturecompensated crystal oscillation circuit 41. The circuit 41 transmits thecompensation signal "S4" on the basis of the AFC data signal "S3". Thecompensation signal "S3" is supplied to the PLL circuit 23 of theconverter 20 to control the voltage controlled oscillation circuit 42.The signal "S3" is also supplied to the quality judgment unit 30 so asto be used as an operation clock for the respective circuits 31 to 34.

A control voltage of the voltage controlled oscillation circuit 42 iscontrolled by the PLL circuit 23, thereby to vary the oscillationfrequency. Then, as described above, the output signal of the voltagecontrolled oscillation circuit 42 is supplied to the frequencydemultipliers 12 and 13, so that information of the AFC data is fed backto the GMSK signal "S1".

Referring to a flow chart of FIG. 2, an operation of the embodiment willbe described below.

When the received GMSK signal "S1" is supplied to the mixer 11 of thequadrature demodulation unit 10 (Step 201), the frequency demultiplyingsignal from the frequency demultiplier 12 is mixed with the GMSK signal"S1" so that the second intermediate frequency signal "S2" is created(Step 202). After being amplified by the amplifier 14, the secondintermediate frequency signal "S2" is supplied to the mixers 16 and 18.After the phase of the second intermediate frequency signal "S2" isshifted by the phase shifter 19, it is amplified by the amplifiers 15and 17 so as to be supplied to the converter 20 as the in-phase signal"I" and the "antiphase signal "Q" (Step 203). The second intermediatefrequency signal "S2" is divided by the amplifier 14 and supplied to theconverter 20 as the electric field strength signal "RSSI".

The in-phase signal "I", the antiphase signal "Q" and the electric fieldstrength signal "RSSI" supplied to the converter 20 are converted to thedigital signals by the A/D conversion circuit 21, so as to be suppliedto the quality judgment unit 30 (Step 204).

When the in-phase signal "I" and the antiphase signal "Q" are suppliedto the mutual-correlation factor calculating circuit 31 of the qualityjudgment unit 30, the amount of interference between the codes iscalculated on the basis of the in-phase signal "I" and the antiphasesignal "Q". The codes interference amount signal "S5" representing theresult of the calculation is supplied to the signal quality calculatingcircuit 32 (Step 205). Subsequently, in the signal quality calculatingcircuit 32, the quality signal "S6" representing the quality of theinput signal by a numerical value is created on the basis of the amountof interference between the codes exhibited by the codes interferenceamount signal "S5" and the electric field strength signal "RSSI", thequality signal "S6" being supplied to the signal quality judging circuit33 (Step 206). Thereafter, the quality of the input signal is ranked onthe basis of the quality signal "S6" supplied to the signal qualityjudging circuit 33. In this connection, the control signal "S7" issupplied so that the AFC data creating circuit 34 performs thecompensation predetermined in correspondence to the rank of the signal(Step 207). When the control signal "S7" is supplied to the AFC datacreating circuit 34, the AFC data is compensated in response to thecontrol signal "S7", so as to supply the AFC data signal(Step 208).

The AFC data signal "S3" created by the AFC data creating circuit 34 isutilized by the mobile communication system body, and also supplied tothe temperature compensated crystal oscillation circuit 41 after it hasbeen converted to the analog signal by the D/A conversion circuit 22(Step 209).

Consequently, the compensation signal "S4" corresponding to the AFC datasignal "S3" is created in the temperature compensated crystaloscillation circuit 41 and supplied to the PLL circuit 23 (Step 210).The voltage controlled oscillation circuit 42 is controlled on the basisof the compensation signal "S4" by the PLL circuit 23, thereby carryingout the automatic frequency control (Step 211).

As described above, according to the automatic frequency control circuitof the present invention, since the frequency is automaticallycontrolled on the basis of the result of judgment of the signal qualityby the quality judgment unit 30, even when Doppler shift or multipassfading occurs during the movement of the mobile communication system,the frequency of the input signal can be compensated in accordance withthe degradation of the quality of the signal. Thus, it is possible toprevent the malfunction of the mobile communication system such asstoppage of the operation of the system.

Although the invention has been illustrated and described with respectto exemplary embodiment thereof, it should be understood by thoseskilled in the art that the foregoing and various other changes,omissions and additions may be made therein and thereto, withoutdeparting from the spirit and scope of the present invention. Therefore,the present invention should not be understood as limited to thespecific embodiment set out above but to include all possibleembodiments which can be embodies within a scope encompassed andequivalents thereof with respect to the feature set out in the appendedclaims.

What is claimed is:
 1. An automatic frequency control circuit installedon a mobile communication system, comprising:an quadrature demodulationmeans for creating an in-phase signal and an antiphase signal byquadrature-demodulating a Gaussian Minimum Shiftkeying signal beingsupplied, and supplying an electric field strength signal exhibiting anelectric field strength of the Gaussian Minimum Shiftkeying signal aswell as said created in-phase and antiphase signals, a quality judgingmeans for judging the quality of the Gaussian Minimum Shiftkeying signalon the basis of said in-phase signal, antiphase signal and electricfield strength signal, and creating an automatic frequency-controllingdata indicating a compensation amount in accordance with the obtainedquality signal so as to supply the same, a conversion means forconverting said in-phase signal, antiphase signal and electric fieldstrength signal supplied from said quadrature demodulation means intodigital signals so as to transfer them to said quality judging means,and converting said automatic frequency-controlling data supplied fromsaid quality judging means into an analog signal, and, a compensatingmeans for compensating the frequency of the Gaussian Minimum Shiftkeyingsignal on the basis of the compensation amount indicated by saidautomatic frequency-controlling data converted into an analog signal bysaid conversion means.
 2. An automatic frequency control circuit as setforth in claim 1, whereinsaid quadrature demodulation means comprisesameans for mixing the Gaussian Minimum Shiftkeying signal converted to afirst intermediate frequency signal and an oscillation signal suppliedfrom said compensating means on the basis of said automaticfrequency-controlling data so as to convert them to a secondintermediate frequency signal, and a means for quadrature-modulating thesecond intermediate frequency signal so as to create said in-phasesignal and antiphase signal.
 3. An automatic frequency control circuitas set forth in claim 1, whereinsaid quality judging means comprisesameans for calculating an amount of interference between codes on thebasis of said in-phase signal and antiphase signal, a means forcalculating the quality of the signal by the combination of said codesinterference amount and said electric field strength signal with theboth as parameter, and a means for supplying said automaticfrequency-controlling data indicating said compensation amount inaccordance with the quality of the signal to said conversion means. 4.An automatic frequency control circuit as set forth in claim 1,wherein:said quadrature demodulation means comprisesa means for mixingthe Gaussian Minimum Shiftkeying signal converted to a firstintermediate frequency signal and an oscillation signal supplied fromsaid compensating means on the basis of said automaticfrequency-controlling data so as to convert them to a secondintermediate frequency signal, and a means for quadrature-modulating thesecond intermediate frequency signal so as to create said in-phasesignal and antiphase signal; and said quality judging means comprisesameans for calculating an amount of interference between codes on thebasis of said in-phase signal and antiphase signal, a means forcalculating the quality of the signal by the combination of said codesinterference amount and said electric field strength signal with theboth as parameter, and a means for supplying said automaticfrequency-controlling data indicating said compensation amount inaccordance with the quality of the signal to said conversion means. 5.An automatic frequency control circuit as set forth in claim 1,whereinsaid quality judging means comprisesa mutual-correlation factorcalculating circuit for calculating the mutual-correlation factor of aninput signal on the basis of said in-phase and antiphase signals tocompute an amount of interference between codes, a signal qualitycalculating circuit for calculating the quality of the signal by thecombination of said codes interference amount and said electric fieldstrength signal with the both as parameter, a signal quality judgingcircuit for ranking the quality of the signal and supplying a controlsignal exhibiting a rank of the corresponding quality signal, and anautomatic frequency-controlling data creating circuit for creating saidautomatic frequency-controlling data on the basis of said controlsignal.
 6. An automatic frequency control circuit as set forth in claim5, whereinsaid mutual-correlation factor calculating circuitobtainseleven mutual-correlation factors by shifting across central continuous16 bits among 26 bits of training sequence codes in one burst of thein-phase signal on the basis of the GSM, selects arbitrary fivemutual-correlation factors from the obtained eleven mutual-correlationfactors to totalize the absolute values thereof, and subtracts a totalof the absolute values of the other six mutual-correlation factors froma total of the absolute values of all the eleven mutual-correlationfactors, except for the five mutual-correlation factors having theabsolute values of which total is maximum, thereby to transmit theobtained value as a codes interference amount signal.
 7. An automaticfrequency control circuit as set forth in claim 5, whereinsaid signalquality calculating circuithaving a table relating a combination of saidcodes interference amount and electric field strength signal to anumerical value predetermined to represent the quality of the inputsignal with the both as parameter, combines said codes interferenceamount calculated by said mutual-correlation factor calculating circuitand said electric field strength signal supplied via said conversionmeans and checks them with said table, thereby to transmit thecorresponding numerical value as a quality signal representing thequality of the corresponding input signal.
 8. An automatic frequencycontrol circuit as set forth in claim 5, whereinsaid signal qualityjudging circuitranks the quality of the input signal calculated by saidsignal quality calculating circuit, and transmits the control signal forcontrolling said automatic frequency-controlling data creating circuitin order to perform the predetermined compensation to said automaticfrequency-controlling data in accordance with the quality rank of thecorresponding signal.
 9. An automatic frequency control circuit as setforth in claim 5, wherein:said mutual-correlation factor calculatingcircuitobtains eleven mutual-correlation factors by shifting acrosscentral continuous 16 bits among 26 bits of training sequence codes inone burst of the in-phase signal on the basis of the GSM, selectsarbitrary five mutual-correlation factors from the obtained elevenmutual-correlation factors to totalize the absolute values thereof, andsubtracts a total of the absolute values of the other sixmutual-correlation factors from a total of the absolute values of allthe eleven mutual-correlation factors, except for the fivemutual-correlation factors having the absolute values of which total ismaximum, thereby to transmit the obtained value as a codes interferenceamount signal; and said signal quality calculating circuithaving a tablerelating a combination of said codes interference amount and electricfield strength signal to a numerical value predetermined to representthe quality of the input signal with the both as parameter, combines theamount of interference between the codes exhibited by said codesinterference amount signal supplied from said mutual-correlation factorcalculating circuit and said electric field strength signal supplied viasaid conversion means and checks them with said table, thereby totransmit the corresponding numerical value as a quality signalrepresenting the quality of the corresponding input signal.
 10. Anautomatic frequency control circuit as set forth in claim 5,wherein:said signal quality calculating circuithaving a table relating acombination of said codes interference amount and electric fieldstrength signal to a numerical value predetermined to represent thequality of the input signal with the both as parameter, combines saidcodes interference amount calculated by said mutual-correlation factorcalculating circuit and said electric field strength signal supplied viasaid conversion means and checks them with said table, thereby totransmit the corresponding numerical value as a quality signalrepresenting the quality of the corresponding input signal; and saidsignal quality judging circuitranks the quality of the input signalexhibited by the quality signal supplied from said signal qualitycalculating circuit, and supplies the control signal for controllingsaid automatic frequency-controlling data creating circuit in order toperform the predetermined compensation to said automaticfrequency-controlling data in accordance with the quality rank of thecorresponding signal.
 11. An automatic frequency control circuit as setforth in claim 5, wherein:said mutual-correlation factor calculatingcircuitobtains eleven mutual-correlation factors by shifting acrosscentral continuous 16 bits among 26 bits of training sequence codes inone burst of the in-phase signal on the basis of the GSM, selectsarbitrary five mutual-correlation factors from the obtained elevenmutual-correlation factors to totalize the absolute values thereof, andsubtracts a total of the absolute values of the other sixmutual-correlation factors from a total of the absolute values of allthe eleven mutual-correlation factors, except for the fivemutual-correlation factors having the absolute values of which total ismaximum, thereby to transmit the obtained value as a codes interferenceamount signal; said signal quality calculating circuithaving a tablerelating a combination of said codes interference amount and electricfield strength signal to a numerical value predetermined to representthe quality of the input signal with the both as parameter, combines theamount of interference between the codes exhibited by said codesinterference amount signal supplied from said mutual-correlation factorcalculating circuit and said electric field strength signal supplied viasaid conversion means and checks them with said table, thereby totransmit the corresponding numerical value as a quality signalrepresenting the quality of the corresponding input signal; and saidsignal quality judging circuitranks the quality of the input signalexhibited by the quality signal supplied from said signal qualitycalculating circuit, and supplies the control signal for controllingsaid automatic frequency-controlling data creating circuit in order toperform the predetermined compensation to said automaticfrequency-controlling data in accordance with the quality rank of thecorresponding signal.
 12. An automatic frequency control circuit as setforth in claim 1, wherein:said compensating means comprisesa voltagecontrolled oscillation circuit for transmitting a predetermined signalwhich is used for the quadrature demodulation of the Gaussian MinimumShiftkeying signal in said quadrature demodulation means, a temperaturecompensated crystal oscillation circuit for creating and supplying acompensation signal on the basis of said automatic frequency-controllingdata, and a phase lock loop circuit for controlling the oscillationfrequency of said voltage controlled oscillation circuit according tothe compensation signal supplied from said temperature compensatedcrystal oscillation circuit; and said quadrature demodulation meanscomprisesa means for mixing the Gaussian Minimum Shiftkeying signalconverted to a first intermediate frequency signal and an oscillationsignal supplied from said voltage controlled oscillation circuit of saidcompensating means so as to convert them to a second intermediatefrequency signal, and a means for quadrature-modulating said secondintermediate frequency signal so as to create said in-phase signal andantiphase signal.
 13. An automatic frequency control circuit as setforth in claim 1, wherein:said quality judging means comprisesamutual-correlation factor calculating circuit for calculating themutual-correlation factor of an input signal on the basis of saidin-phase and antiphase signals to compute an amount of interferencebetween codes, a signal quality calculating circuit for calculating thequality of the signal by the combination of said codes interferenceamount and said electric field strength signal with the both asparameter, a signal quality judging circuit for ranking the quality ofthe signal and supplying a control signal exhibiting a rank of thecorresponding quality signal, and an Automatic frequency-controllingdata creating circuit for creating said automatic frequency-controllingdata on the basis of said control signal; said compensating meanscomprisesa voltage controlled oscillation circuit for transmitting apredetermined signal which is used for the quadrature demodulation ofthe Gaussian Minimum Shiftkeying signal in said quadrature demodulationmeans, a temperature compensated crystal oscillation circuit forcreating and supplying a compensation signal on the basis of saidautomatic frequency-controlling data, and a phase lock loop circuit forcontrolling the oscillation frequency of said voltage controlledoscillation circuit according to the compensation signal supplied fromsaid temperature compensated crystal oscillation circuit; and saidquadrature demodulation means comprisesa mixer for mixing the GaussianMinimum Shiftkeying signal converted to a first intermediate frequencysignal and an oscillation signal supplied from said voltage controlledoscillation circuit of said compensating means so as to convert them toa second intermediate frequency signal, and mixers or a phase shifterfor quadrature-modulating said second intermediate frequency signal soas to create said in-phase signal and antiphase signal.